The invention relates to a strain relief device which protects the user of electrical power tools, or other electrical devices, by protecting the electrical supply line from straining forces which may act upon the line where it enters the electrical device.
Such devices are well known in the art, but the previously known devices have disadvantages. One such device is described in U.S. Pat. No. 3,546,502. This device has a clamping ring secured around the electrical supply cord by two screws. The screws press the ring against the electrical line forcing it into a depression in the tool or appliance housing. This device is disadvantageous since the electrical line must be secured after it is placed near the depression to permit the clamping ring to be placed over the connection and then screwed tightly to permanently attach the ring. This process is undesirably time consuming, even if a mounting device is used to assist the installation. An additional disadvantage is the failure due to permanent deformation of the above-described device over a length of time, i.e. the device eventually plastically deforms the electrical line and thus no longer adequately secures the line.
Another well known device, described in U.S. Pat. No. DE. 1,285,588, has a sleeve with a conical hole inside of which is placed a frustoconical clamping body capable of longitudinal movement and a coiled spring that pushes the clamping body toward the narrower end of the hole. The electrical line is attached using a special tool to press the clamping body against the spring. The line is then inserted into the gap formed between the tool housing and the clamping body. When the line is placed under a strain, both the line and the clamping body move toward the narrower end of the hole until they become wedged. The originally round cross-section of the electrical line becomes deformed thereby to a kidney-shaped cross-section due to the contact of the clamping body with the line. A disadvantage of this device is that it permits the line to be damaged by strain forces that are of high magnitude and long duration. Another disadvantage is that the device eliminates only one degree of freedom of the line's motion, i.e. longitudinal motion out of the housing. If instead of a strain force, the line is subjected to a pushing force the line is free to move into the housing. Yet another disadvantage of this device is the impossibility of inserting cable ends provided with connecting lugs or terminals into the housing in the direction counter to the spring force.